As market demand drives the evolution of portable communication devices, such as smartphones and two-way radios, engineering limitations determine the rate of progress. New innovation is required to support a next-generation of communication devices that offer improved functionality. A particular area in which progress can be made in the state of the art is in better managing the specific absorption rate (SAR) associated with communication devices. SAR is a measure of the amount of radio frequency energy absorbed by the body when using such devices. Currently, the maximum SAR level allowed by the Federal Communications Commission (FCC) is 1.6 watts per kilogram.
Because of their small form factor, portable communication devices today typically have small antennas that are completely enclosed within the devices' outer shell. As a result, more of a user's body covers the antenna when the device is held in user-proximal positions, such as in the hand or against the user's head. In these positions, the increased area of exposure translates into the user's body intercepting a greater amount of transmitted energy while the antenna is radiating. The current solution is to use sensor and application data to determine when the communication device is in a user-proximal position and then to cut back on the transmitted power level to reduce SAR. A difficulty presents itself, however, when the data used to ascertain the user's body position is no longer trustworthy. This is the case when data processing related to the radio frequency (RF) subsystem is performed by an application processor that is unlocked. When the processor is unlocked, the user has the ability to “tweak” or alter previously secure hardware and/or software associated with the processor—in some cases with the goal of looking for a performance gain.
Existing communication devices employ a maximum cutback of the transmitted power level when the application processor is unlocked. Once the application processor is unlocked, the power is cut back all the time. When the data concerning the user's body position is no longer reliable, the power level needs to be low enough to ensure that SAR will be within tolerance for every possible position. While this “worst-case-scenario” method works, it comes at the price of unnecessarily diminished performance.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. In addition, the description and drawings do not necessarily require the order illustrated. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.